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| Reflecting
telescopes |
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These
are also known as
Newtonian telescopes. They have a concave primary mirror, coated
with aluminum and protected by a coating of SiO. The mirror is at
the back end of the tube. A secondary mirror, which is flat,
smaller in size and also aluminized, is placed nearer to the
front of the tube at 45 degrees. This mirror reflects the image
out of the tube at a suitable distance. The image is then
captured and magnified using an eyepiece.
The performance achieved by a
Newtonian reflector is dependent on the quality of the optics and
the mechanical alignments. Since it is only a mirror system, the
only type of aberration (image defects) that can be introduced is
spherical aberration due to the concave mirror. It is completely
free from chromatic (color) aberration. All our primary mirrors
are specially figured by hand to get a good surface accuracy.
Each and every mirror is tested using the Foucault Knife Edge
test which can detect surface defects up to millionth of an inch. The
secondary mirrors are precision
flats made to an accuracy of lambda/4 (0.2 microns).
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